Flashback prevention in gas burners



J July 28, 1953 A. J. LAMPERT FLASHBACK PREVENTION IN GAS BURNERS Filed Oct. 17, 1950 ALBERT J. LAMPERT,

' INVENTOR.

HUEBNER,BHLR,WORREL 8 HERZIG 1 v A T TORNEYS.

Patented July 28, 1953 v UNITED STATES PATENT OFFICE FLASHBACK PREVENTION IN GAS BURNERS Albert .l'. Lampert, Walnut,; Calif., assignor to Rheem Manufacturing Company, Richmond, Calif., a corporation of California I Application October 17, 1950, Serial No. 190,455

Claims. (01. 126 8 5) Thisinvention relates. to prevention of flashback and consequent, extinction noise when agas burner is turned off.

:It. is an objectof this invention to prevent flashback from burner ports into the conduit feeding the burner with combustion gas.

. It is another object of this invention to preven extinction explosion resulting from flashback when the gas supply to a-burner is cut off. .Elashback prevention means have taken the formof screens or grids interposed across the conduit leading to the burner. These screens are generally within or adjacent the burner head or member. There are two theories as to how such screens operate. One theory is that the screens have. suiflcientheat capacity to absorb the flame as it travels, .or flashes, back in the conduit, thereby lowering the temperature below the ignition point and preventingpontinued passage of the. flame. Another theory,- somewhat, more widely held, is, that suchscreena'by their inherent restricting properties, accelerate the forward flow of gas and air 'to a velocity greater than the.v propagation velocity of the flashing-back flame; Thus, as the flame reaches the screen it encounters a region where the gasflow in a forward direction is greater than the flame velocity backward andthe flame is consequently extinguished.

g-Regardless of the theory adopted, it is an in- I herentproperty ofsuch screens that they serve to-restrict the; flow of gas with the consequent disadvantage of loss of pressure at the burner hea a It is another object of this invention to prevent flashback in gas burners without introducingrestrictions of any type in thenormal flow of gas tothe burner head. H

' :It:has also beenproposed to lead the incoming gas through a tortuous path, thereby providing an elevated trap in which the gas tends to gather, thus blockingqiany residual flow of air-gas mixtur'e, :which is the initiating cause of the flashback :in the first place. This tortuous path likewise. introduces impedance ,to the flow ofgas to the burner head with resulting loss ;in,pressure atthe head: Itis a further object of this invention to prevent flashback without introducing anytypelof impedance tothe gas flow, thereby maintaining full pressure at the burner head. accordancewith the above objects and with others which will become apparent throughout the ensuing specification, the instant invention =w111 now be-described A typical gas burner consists of a burner mem her, or head, having outlet ports at whichthe air-gas mixture burns to heat some type or heater, or heat exchanger. Suitable conduit means communicates with the head to conduct air-gas mixture thereto. It is customary to feed combustion gas to the conduit means through a nozzle, or other orifice, adjacent which are a number of apertures by means of which combustion air, in this case primary air, is aspirated by the well-known Bernoulli principle into the conduit means. Thus, a mixture oi air and gas is fed through the conduit means into the burner head and out the burner ports where combustion takes place. I v p When the shut-off valve in the gas line is closed, flow of gas from the nozzle ceases. The momentum of the air-gas mixture already flowingin'the conduit continues to carry it toward the burner head and continues to draw primary air in through the apertures. Thus, for a short time immediately following closing of the gas valve, a progressively rarer air-gas mixture is fed to the burner head; that is, the ratio of gas to air progressively decreases.

Thevelocity of flame propagation increases as the gas-to-air ratio decreases. Since the residual air-gas mixture is steadily slowing down, the two efiects combine until a point is reached where the flame propagation velocity exceeds the'flow velocity of the mixture. At this point the flame at the burner penetrates the outlet ports and propagates backwardly in the gas conduit until it reaches the nozzle, at which time all the airgas mixture has been burned. This phenomenon is known as flashback and is generally attended by a loud popping or extinction noise.

In accordance with the instant invention flash- .back is prevented-not by blocking the flashback flame, as with a screen-but by removing the residual air-gas mixture rapidly from the burner member and the conduit, thereby leavingnothing to be burned. This is effected by placing a conduit, or flashback prevention tube, in communication with the gas conduit, preferably adjacent the gas nozzle and air apertures The flashback prevention tube is positioned with at least a portion thereof extending upwardly in heat receiving disposition with respect to the heater which is heated by the flame at the burner head. The flacsihback prevention tube is open at its upper en When the apparatus is in operation,.the flashback prevention tube is heated by the heater so that the air therein tends to rise. There is a 3 contrary tendency of the air in the flashback prevention tube to be drawn downwardly into the gas conduit because of the aspirating action of the gas nozzle. The net effect is, with proper design, a balance in which the air in the flashback prevention tube is substantially dormant.

Nhen the gas flow is shut ofi by closing the gas valve, the aspirating influence within the flashback prevention tube immediately ceases. The convection tendency of the heated air now pulls the air therein upwardly and out the open end. This creates a suction effect which, overcoming the residual momentum of the air-gas mixture in the gas conduit, rapidly draws the mixture out of the conduit and up the flashback prevention tube. The burner head and conduit are thus emptied of combustible mixture so that no flashback occurs.

In accordance with the above description a specific embodiment of the instant invention will now be described in conjunction with the accompanying drawings wherein:

Figure 1 is an elevational view of apparatus embodying the instant invention;

Figure 2 is a detail view showing the burner and bottom portion of the flashback prevention tube; and

Figure 3 is a sectional view taken on line 3-3 of Figure 2.

Referring to the drawings, H designates a burner member, or head, having the usual outlet ports at the top thereof at which flames l2 burn. Conduit means in the form of a burner conduit l 3 communicates with the burner head I l and terminates at an aspirator housing [4. Projecting into the housing M is a gas nozzle 16 connected to a gas line ll by means of which combustible gas under pressure is fed to the nozzle 16. A valve E3 is interposed in the line I! to control the flow therethrough. Heater means 4'.

In accordance with the instant invention a second conduit in the form of a flashback prevention tube 22 communicates with the housing M at the top thereof and extends upwardly adjacent the heater [9, so that the air in the tube 22 is heated from the heater [9. The tube 22 is open at its upper end.

Operation Operation of the instant invention is as follows:

When gas valve I8 is turned on, gas flows through the nozzle 16 into the conduit I3, aspirating primary air into the housing M and conduit l3 through the apertures 25. This combustible air-gas mixture flows from the burner member ll through the ports thereof and produces, when ignited, the heating flames 42. The

hot gases from the flames 1-2 pass upwardly and heat the heater [9.

As the heater l9 warms up it also warms the air in the nearby flashback prevention tube 22 In the initial stages of operation, air flows downwardly through the tube 22 into the conduit [3 because of the aspirating effect of the nozzle :6.

As the-tube 22 heats up, however, a balance is created wherein the upward convection force in the tube 22 balances the downward aspirating force from the nozzle l6, so that air in the tube 22 is substantially dormant. As a matter of safety, to insure against gas flow out of the upper end of the tube 22, it is preferred to design the structure so that the net tendency is a slight downflow in the tube 22, thereby precluding any escape of combustion gas.

When the valve 18 is suddenly closed, as is the case with automatic solenoid-operated valves, the aspirating effect at the nozzle [6 abruptly ceases. Residual momentum of the air-gas mixture in the conduit [3 continues, however, to draw in atmospheric air through the apertures 2 I, thereby thinning out the mixture in the conduit [3 and raising its flame propagation velocity.

However, as soon as gas flow ceases from the nozzle :6, the convection tendency in the tube 22 immediately starts to draw the air-gas mixture out of the housing l4 and conduit 13. The residual momentum of the air-gas mixture in conduit I3 is thus almost immediately arrested, and the flow is reversed back toward the housing l4 and up the pipe 22. Thus, before the mixture in the burner member II can be thinned out to the flashback point, the entire combustible mixture in the housing I3 is emptied through the tube 22 and flashback is efiectively prevented.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent methods and apparatus.

What is claimed is:

1; In a gas burner including a burner member having outlet port means, conduit means communicating with said burner member adapted to feed gas thereto, an apertured aspirator housing formed on the end of said conduit means, a nozzle extending into said housing and adapted to be connected to a source of combustion gas, whereby to draw in combustion air through the housing apertures as it flows to said burner member, and heater means positioned to be heated by gas burned at said burner member, the combination of a flashback prevention tube communicating at one end with said housing adjacent the mouth of said nozzle and extending upwardly in-heat receiving disposition with respect to said heater means, the upper end of said tube being open to atmosphere.

2. In a gas burner including a burner member having outlet port means, first conduit means communicating with said burner member adapted to feed gas thereto, orifice means positioned to direct combustible gas into said first conduit means, said first conduit means having a combustion air inlet opening adjacent said orifice means, and heater means positioned to be heated by gas burned at said burner member, the combination of second conduit means communicating at one end with said first conduit means adjacent said orifice means and being open at the other end, and extending upwardly in heat receiving disposition with respect to said heater means.

3. In a gas burner including a burner member having outlet port means, first conduit means communicating with said burner member adapted to feed gas thereto, orifice means positioned to direct combustible gas into said first conduit means, said first conduit means having a combustion air inlet opening adjacent said orifice means, and heater means positioned to be heated by gas burned at said burner member, the combination of second conduit means communicating with said first conduit means adjacent said orifice means and being open at one end, at least a portion of said second conduit means extending upwardly in heat receiving disposition with respect to said heater means.

4. In a gas burner including a burner member having outlet port means, first conduit means communicating with said burner member adapted to feed gas thereto, orifice means communicating with said first conduit means and adapted to be connected to a source of combustion gas, and heater means positioned to be heated by gas burned at said burner member, the combination of second conduit means communicating at one end with said first conduit means adjacent said orifice means, extending upwardly in heat receiving disposition with respect to said heater means, and terminating in an open end disposed exteriorly of said heater means and out of communication therewith.

5. In a gas burner including a burner member having outlet port means, first conduit means communicating with said burner member adapted to feed. gas thereto, orifice means communicating with said first conduit means and adapted to be connected to a source of combustion gas, and heater means positioned to be heated by gas burned at said burner member, the combination of second conduit means communicating at one end with said first conduit means adjacent said orifice means, at least a portion of said second conduit means extending upwardly in heat receiving disposition with respect to said heater means, said second conduit means terminating in an open end disposed exteriorly of said heater means and out of communication therewith.

ALBERT J. LAMPERT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 416,130 Walters Nov. 26, 1889 763,057 Hutchinson June 21, 1904 1,074,157 Beler Sept. 30, 1913 1,079,327 Chadborn Nov. 25, 1913 1,105,987 McSorley Aug. 4, 1914 1,562,590 Rodgers Nov. 24, 1925 2,062,605 Peters Dec. 1, 1936 2,200,264 Dennis et a1. May 14, 1940 

